Method for maintaining continuity of a network signal path extending along a backplane

ABSTRACT

A method for maintaining continuity of a network signal path extending along a backplane includes providing a bypass signal circuit compatible with the network signal path and being electrically connected in series with the first and second portions of the network signal path. The bypass signal circuit includes a normally open circuit portion and an electrical contact movable with respect to the bypass signal circuit. An electrical contact is mechanically moved out of contact with the bypass signal circuit and moved mechanically into contact with the bypass signal circuit in response to the function module being detached from or attached to the function module electrical connector and not in response to an electrical control signal.

RELATED APPLICATIONS

This application is a division of and claims priority to pending U.S.patent application Ser. No. 16/645,606 “Mechanical Bypass SwitchAssembly for a Backplane” filed on Mar. 9, 2020, which in turn is aUnited States nationalization of pending Patent Cooperation TreatyApplication PCT/US2018/051286 “Mechanical Bypass Switch Assembly for aBackplane” filed on Sep. 17, 2018, which priority applications are bothincorporated by reference as if fully set forth herein.

FIELD OF THE DISCLOSURE

The disclosure relates generally to networks utilizing a backplane thatprovides an electrically conductive signal path through a number ofelectrical connectors attached to the backplane, and in particular, to amethod for maintaining continuity of the signal path along thebackplane.

BACKGROUND OF THE DISCLOSURE

Industrial control networks often utilize an electrically conductivesignal path that transmits data, power, or both power and data signalsalong a network. The signal path may be arranged in different networktopologies, including a bus network topology (in which the signal pathextends along a linear or branched path) or a ring network topology (inwhich the signal path extends along a closed loop). In some ringnetworks the signal path includes two rings that can independently carrythe signal and provide redundancy in the event of a break in the signalpath.

Signal paths may be formed on a backplane that carries and connectsmultiple function modules to the network. A function module may processdata read from the network, may write data to the network, or mayperform other tasks.

The signal path extends through the function modules attached to thebackplane. An active function module is capable of reading and/orwriting data from or to the signal path. A passive function modulemerely passes the signal path through the function module to maintainsignal path continuity without reading or writing data.

The backplane may be a monolithic backplane formed from a single printedcircuit board. The printed circuit board may connect multiple functionmodules to the signal path. Alternatively the backplane may be formedfrom a number of backplane modules, each module including a printedcircuit board. Left and right electrical connectors on the sides of eachprinted circuit board interconnect the backplane modules and enable thesize of the backplane formed by the backplane modules to vary in use.

The signal path on a printed circuit board may in some networks consistof a single electrically conductive path that corresponds totransmitting the signal along a single wire. The signal path on aprinted circuit board may in other networks consist of multipleelectrically conductive paths that correspond to transmitting the signalalong the wires of a multi-wire cable, each conductive pathcorresponding to a different wire. For example, the signal path of anEthernet based industrial control network may be formed as fourelectrically conductive paths corresponding to the wires of a 4-wireEthernet cable.

The printed circuit board of a monolithic backplane may carry multiplefunction module electrical connectors that removably mount the functionmodules to the printed circuit board. The printed circuit boards ofmodular backplanes typically carry a single function module electricalconnector.

A function module electrical connector includes an electricallyconductive signal path that is connected to the signal path of theprinted circuit board. The signal path through the function moduleelectrical connector is normally open if a function module is notattached to the function module electrical connector. The functionmodule includes an electrical connector that mates with the functionmodule electrical connector and closes the signal path to enable thesignal path to extend through the function module.

As illustrated below, the signal path break at the function moduleelectrical connector which has a function module removed can preventdata transmission to other function modules on the network.

FIG. 24 illustrates a portion of an industrial control network 510utilizing a monolithic backplane 512 formed from a single printedcircuit board and a number of like function module electrical connectors514 attached to the backplane. Each function module electrical connectoris intended to receive a respective function module 516 that iselectrically and at least partially mechanically connected to thebackplane through the connector.

FIG. 24 illustrates the backplane 512, function module electricalconnectors 514, and function modules 516 transmitting an Ethernet signalpath S along a portion of an industrial control network configured as abus topology. Data passes in series through each function module, andthen out from the backplane. The backplane may form part of a signalpath for a larger network topology.

The signal path S includes four parallel electrically conductive paths,the paths corresponding to the wires of a 4-wire Ethernet cable.

If a function module 516 is removed from a function module electricalconnector 514, communication of the Ethernet signal stream withdownstream function modules is broken by an open circuit in the signalpath at the function module electrical connector. See FIG. 25 in which afunction module has been removed from a connector. The signal break isindicated by the “X” in the figure.

To enable communication with downstream function modules 516 even if afunction module is removed from a function module electrical connector514, it is known to place software-controlled bypass switch assemblies520 in the signal path. See FIG. 26. Each bypass switch assembly isassociated with a respective function module electrical connector. Abypass switch assembly includes a signal bypass circuit 522 wired in thesignal path in parallel with the signal path of the function moduleelectrical connector, and a bypass switch 524 in the bypass circuit thatselectively opens and closes the signal bypass circuit.

As seen in FIG. 26, the bypass switch 524 associated with a functionalmodule electrical connector is closed if there is no function moduleattached to the function module electrical connector. The normallyclosed switch enables the signal path S to bypass the open functionmodule electrical connector 514 and continue downstream past the openconnector.

The bypass switch 524 is open when there is a function module attachedto the function module electrical connector. The signal path S extendsthrough the function module electrical connector and through thefunction module 516 attached to the connector.

Bypass switches for backplanes conveying network signals areconventionally formed as electrical devices that open or close undersoftware control in response to an electrical control signal. See, forexample, Monse et al. U.S. Pat. No. 7,894,336 and Noel et al. US PatentApplication Publication 2011/0145433.

There is a need for reliability and performance reasons, however, for amethod for mechanically maintaining continuity of a network signal pathwhen attaching or removing functional modules to or from function moduleelectrical connectors attached to the backplane that does not operate inresponse to an electrical control signal. The method shouldautomatically close the bypass switch if a function module is removedfrom the function module electrical connector, and should automaticallyopen the bypass switch when a function module is operatively connectedto the function module electrical connector, and should be usable withdifferent network topologies and with signal paths having differentnumbers of conductive paths.

SUMMARY OF THE DISCLOSURE

Disclosed is a method for maintaining continuity of a network signalpath extending along a backplane, the backplane having a function moduleelectrical connector attached to the backplane being configured forselectively attaching or detaching a function module to or from thebackplane. The network signal path extends through the function moduleelectrical connector and through the function module when the functionmodule is attached to the function module electrical connector. Thenetwork signal path is open at the functional module electricalconnector between first and second portions of the network signal pathof the backplane when the function module is not attached to thebackplane.

The disclosed method includes providing a bypass signal circuitcompatible with the network signal path and being electrically connectedin series with the first and second portions of the network signal path,the bypass signal circuit including a normally open circuit portion andan electrical contact movable with respect to the bypass signal circuit.

The electrical contact being out of contact with the bypass signalcircuit is mechanically moved into contact with the bypass signalcircuit in response to the function module being detached from thefunction module electrical connector and not in response to anelectrical control signal. The electrical contact when in contact withthe bypass signal circuit closes the bypass signal circuit and therebyenables the bypass signal circuit to close the network signal pathbetween the first and second portions of the network signal path.

mechanically moving The electrical contact being in contact with thebypass signal circuit is mechanically moved out of contact with thebypass electrical circuit in response to the function module beingattached to the function module electrical connector and not in responseto an electrical control signal. The bypass electrical circuit is openwhen the electrical contact is out of contact with the bypass electricalcircuit whereby the first and second portions of the network signal pathare electrically connected by the network signal path extending throughthe function module electrical connector and the functional module andnot by the bypass signal circuit.

Also disclosed is a purely mechanical bypass switch assembly forperforming the disclosed method for use in networks utilizing abackplane that provides a signal path through a number of functionalmodule electrical connectors attached to the backplane. The mechanicalbypass switch assembly automatically closes the bypass switch if afunction module is removed from the function module electricalconnector, and automatically opens the bypass switch when a functionmodule is connected to the function module electrical connector. Themechanical bypass switch assembly is usable with different networktopologies and with signal paths having different numbers of conductivepaths.

A backplane or backplane module utilizing the mechanical bypass switchassembly includes a printed circuit board, a function module electricalconnector capable of being removably connected to a function module formaking electrical connections therebetween, and a bypass circuitassembly. The printed circuit board has a first side, an opposite secondside, and an electrically conductive network signal path.

The function module electrical connector is attached to the first sideof the printed circuit board and includes an electrically conductivesignal path in series with the network signal path of the printedcircuit board. The network signal path has an open portion between firstand second portions of the network signal path when no function moduleis connected to the function module electrical connector.

The bypass circuit assembly includes a bypass circuit, a mechanicallyactuated bypass circuit switch, and an actuator. The bypass circuitforms a portion of the printed circuit board and includes anelectrically conductive bypass signal path and first and second sets ofelectrical terminals. The bypass signal path is connected in seriesbetween the first and second portions of the network signal path, withthe bypass signal path extending in parallel across the open portion ofthe network signal path. The bypass signal path includes a first portionconnected to the first portion of the network signal path, a secondportion connected to the second portion of the network signal path, andan open portion between the first and second portions of the bypasssignal path.

The first portion of the bypass signal path includes the first set ofelectrical terminals and the second portion of the bypass signal pathincludes the second set of electrical terminals. The first and secondsets of electrical terminals are not in electrical continuity with oneanother and are located on the second side of the printed circuit board.

The electrical contact is on the second side of the printed circuitboard and is movable with respect to the printed circuit board betweenspaced-apart closed and opened positions. The electrical contact engagesthe first and second sets of electrical terminals of the bypass circuitand thereby closes the bypass signal path when the electrical contact isin the closed position. The electrical contact is spaced apart from anddoes not engage the first and second sets of electrical terminals of thebypass circuit when the electrical contact is in the opened position.

The actuator is connected to the electrical contact and is conjointlymovable with the electrical contact. The actuator extends from thesecond side of the printed circuit board and through the printed circuitboard to a free end of the actuator located on the first side of theprinted circuit board and spaced away from the printed circuit boardwhen the electrical contact is in the closed position. A force appliedto the free end of the actuator when the electrical contact is in theclosed position urging the free end of the actuator towards the printedcircuit board also urges the electrical contact towards the openedposition of the electrical contact.

In embodiments of the disclosed bypass circuit switch assembly thebypass switch includes a number of electrical contacts that open andclose respective conductive paths of the network signal path. Thenetwork signal path for example may have four conductive pathscorresponding to the four wires of a standard four-wire Ethernet cablethat form part of a bus network topology or a ring network topology.

In yet other embodiments of the disclosed bypass switch assembly theswitch assembly may be located in a housing that also houses the printedcircuit board and attaches the printed circuit board and the bypassswitch assembly to a DIN rail.

In embodiments of the disclosed bypass switch assembly the electricalcontact is held by a contact holder. The contact holder is urged by aspring towards the closed position of the electrical contact, causingthe bypass switch to be a normally closed switch. In yet otherembodiments of the disclosed bypass switch assembly the contact holderholds two or more electrical contacts.

Other objects and features of the disclosure will become apparent as thedescription proceeds, especially when taken in conjunction with theaccompanying drawing sheets illustrating one or more illustrativeembodiments.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a perspective view of a backplane module having a firstembodiment mechanical bypass switch assembly, the backplane moduleattached to a DIN rail.

FIG. 2 is a top view of the backplane module shown in FIG. 1.

FIG. 3 is a side view of the backplane module shown in FIG. 1.

FIG. 4 is a schematic side view of the signal path and mechanical bypassswitch assembly of the backplane module shown in FIG. 1.

FIG. 5 is a schematic view taken along lines 5-5 of FIG. 4.

FIG. 6 is a sectional view taken along lines 6-6 of FIG. 2.

FIG. 7 is a sectional view taken along lines 7-7 of FIG. 2.

FIG. 8 is a sectional view taken along lines 8-8 of FIG. 3.

FIG. 9 is similar to FIG. 1 but with a function module attached to thebackplane module.

FIG. 10 is similar to FIG. 2 but with a function module attached to thebackplane module.

FIG. 11 is a sectional view taken along lines 11-11 of FIG. 10.

FIG. 12 is a perspective view of a backplane module having a secondembodiment mechanical bypass switch assembly, the backplane moduleattached to a DIN rail.

FIG. 13 is a top view of the backplane module shown in FIG. 12.

FIG. 14 is a side view of the backplane module shown in FIG. 12.

FIG. 15 is a sectional view taken along lines 15-15 of FIG. 13.

FIG. 16 is a sectional view taken along lines 16-16 of FIG. 13.

FIG. 17 is a sectional view taken along lines 17-17 of FIG. 14.

FIG. 18 is similar to FIG. 12 but with a function module attached to thebackplane module.

FIG. 19 is similar to FIG. 13 but with a function module attached to thebackplane module.

FIG. 20 is a sectional view taken along lines 20-20 of FIG. 19.

FIG. 21 is a view similar to FIG. 5 but with the bypass switch assemblybeing used in the ring topology network shown in FIGS. 25-27.

FIG. 22 is a side view of a second embodiment electrical contact havingan end attached to the printed circuit board.

FIG. 23 is a side view of a third embodiment electrical contact havingan integral actuator member.

FIGS. 24-26 are schematic views of a prior art backplane defining a busnetwork topology and having software-controlled bypass switchassemblies.

FIGS. 27-29 are schematic views of a prior art backplane defining aportion of a ring network topology.

DETAILED DESCRIPTION

FIGS. 1-8 illustrate a backplane module 110 used for forming a modularbackplane of an Ethernet-based process control network. The backplanemodule includes a printed circuit board 112 that forms a portion of thebackplane, and a function module electrical connector 114 for connectinga function module to the printed circuit board. The function moduleelectrical connector is located on an upper side 115 of the printedcircuit board.

A left electrical connector 116 and a right electrical connector 118electrically connect the printed circuit board 112 to the printedcircuit boards of adjacent left or right backplane modules. An Ethernetsignal stream S (see FIG. 4) is communicated between one side of theprinted circuit board 112 and the left electrical connector and iscommunicated between the other side of the printed circuit board and theright electrical connector. The signal stream S forms part of a busnetwork topology as shown in FIG. 22. A function module electricalconnector 114 is disposed in the signal stream between the left andright electrical connectors.

The printed circuit board 112 is housed in a plastic housing 120. Thehousing includes a top cover 122, a bottom wall 124 and opposing pairsof side walls 126 integrally formed with the bottom wall. The housingcover and walls cooperatively define an interior volume of the housing.The housing top cover attaches to the housing side walls by housinglatch arms 128, 130.

The illustrated backplane module 110 is shown mounted on a conventionalDIN rail 132. Pairs of DIN rail mounting latches 134, 136 extend fromopposite sides of the housing top cover 122 and attach the housing 120to the flanges 138 of the DIN rail as best seen in FIG. 7. The printedcircuit board 112 is located between the housing top cover and the DINrail flanges. When the housing is attached to the DIN rail the housingside walls extend into the DIN rail recess 140 formed between the DINrail flanges.

The housing top cover 122 is closely spaced above the upper surface 115of the printed circuit board 112. The top cover includes a flat, planarportion 144 that overlays the printed circuit board and a functionmodule electrical connector housing portion 146 that receives thefunction module electrical connector 114. The connector housing portionextends upwardly away from the printed circuit board beyond theelectrical connector 114 and defines a receptacle 148 located above theelectrical connector 114 that assists in guiding attachment of afunction module with the electrical connector 114.

As shown schematically in FIGS. 4 and 5, the backplane module includes abypass switch assembly 150 in the Ethernet signal stream S having anormally-open signal bypass circuit 152 and a mechanically-operatedswitch assembly 154 in the bypass circuit.

The bypass switch assembly 150 is operatively equivalent to the bypassswitch assembly 520 shown in FIG. 23. That is, the bypass switchassembly 150 joins two respective ends of an open circuit portion of abus topology.

The bypass circuit is formed on the printed circuit board 112 andincludes a set of exposed contact terminals 156, 158 located atrespective open ends of the bypass circuit. The contact terminals 156,158 are located on the bottom side 160 of the printed circuit board fromthe function module electrical connector 114 and are disposed inside thehousing 120. The mechanically-operated bypass switch assembly 154 isalso located inside the housing and operates to open and close thebypass circuit.

The Ethernet signal stream S of the illustrated backplane module 110includes conductive paths carried by the printed circuit board 112corresponding to the four wires of a conventional four-wire Ethernetcable. The signal stream S is defined by the four conductive paths Sa,Sb, Sc, and Sd formed on the printed circuit board and corresponding torespective wires of the Ethernet cable. See FIG. 5.

The signal bypass circuit 152 is defined by the four normally openconductive paths 152 a, 152 b, 152 c, 152 d that each bypass arespective conductive path of the signal path S along a bus network oreach interconnect corresponding conductive paths of the two rings R1 andR2.

The contact terminals 156, 158 are formed by respective sets of exposedcontact terminals 156 a-156 d and 158 a-158 d located on the bottom sideof the printed circuit board. The four pairs of contact terminals 156,158 in the illustrated embodiment are formed as four pairs of contactpads (156 a, 158 a), (156 b, 158 b), (156 c, 158 c), and (156 d, 158 d)that are spaced apart transverse to the DIN rail axis. Each pair of pads156, 158 are spaced apart parallel with the DIN rail axis as best seenin FIG. 8.

The mechanically-operated bypass switch assembly 154 includes fourswitches (described in more detail below), each switch associated with arespective pair of contact pads 156, 158 to open and close a respectiveconductive path 152.

Construction of the mechanically-operated bypass switch assembly 154 isdescribed next and is best seen in FIGS. 6-8. A contact holder 162 isdisposed beneath the pairs of contact pads 156, 158. The contact holderis formed from an electrically insulating polymer. The contact holdercarries four electrical contacts 164 formed as spaced apart, like springcontacts 164 a, 164 b, 164 c, 164 d. Each spring contact is associatedwith a respect pair of contact pads (156 a, 158 a), (156 b, 158 b), (156c, 158 c), and (156 d, 158 d). Each spring contact includes a pair ofbent spring arms 166 a, 166 b extending away from each other in oppositedirections along the DIN rail axis. Each spring arm 166 includes acurved contact nose 168 that faces the respective contact pad on theprinted circuit board.

The contact holder 162 is movably mounted in the housing 120 below theprinted circuit board 112 for translation towards and away from theprinted circuit board. Translation of the contact holder causescorresponding conjoint translation of the spring contacts 164 carried bythe contact holder. The contact holder is moveable between a closedposition shown in FIG. 6 and an opened position (seen best in FIG. 11).Pairs of interior planar guide walls 170 extend into the housing fromthe housing side walls and are closely received into correspondingnarrow slots 172 formed on the ends of the contact holder.

When the contact holder 162 is in the closed position the contact holderis closest to the printed circuit board 112 with the contact noses 168in contact with the corresponding contact pads 156 or contact pads 158.Each spring contact 164 a, 164 b, 164 c, 164 d thereby electricallyconnects the respective pairs of contact pads associated with the springcontact and thereby closes a respective signal bypass circuit 152.

The guide walls 170 and the contact holder slots 172 assist in resistingcocking or jamming of the contact holder 162 caused by the spring forcestransmitted to the contact holder from the spring contacts while thecontact holder is moving relative to the printed circuit board 120, andwhen the contact holder in its closed position.

The contact holder 162 moves away from the printed circuit board 112when moving from the closed position to the opened position of thecontact holder. When the contact holder is in the opened position thespring contacts 164 are spaced away from the contact pads 156, 158 andthe contact noses 168 are spaced away from the contact pads by an airgap. The signal bypass 152 is opened and does not carry a bypass signal.

A spring assembly 174 is disposed inside the housing 120 that urges thecontact holder 162 to the closed position. The spring assembly includesa pair of compression springs 176 mounted on elongate posts 178 definedby the bottom wall of the housing. The springs engage against flat lowerabutment surfaces 180 of the contact holder. The compressed length andgenerated spring force of the springs 176 is defined by the distancebetween the abutment surfaces 180 and the housing lower wall 124.

The electrical contacts 164 are located between the springs.

A pair of actuators 182 are used in tandem to drive the contact holder162 from the closed position to the opened position. The actuators areelongate members each integrally formed with the contact holder 162 thatextend upwardly away from respective surfaces 180 of the contact member.See FIG. 7. The actuators extend freely through corresponding alignedthrough holes formed in and extending through the printed circuit board112 and the housing top cover planar portion 144. The actuators arespaced a uniform distance from and relatively close to the side of thefunction module electrical connector housing portion 146 facing theright electrical connector 118.

The actuators 182 extend out of the housing 120 to flat, generallyco-planar upper end surfaces 184 that are generally parallel with theflat cover portion 144.

FIGS. 9-11 illustrate the backplane module 110 with a function module310 operatively attached to the backplane module 110. The functionmodule includes a backplane electrical connector 312 that interconnectswith the function module electrical connector 114 of the backplanemodule. To simplify the drawings, the electronic components of thefunction module other than the backplane electrical connector areomitted.

Attaching the function module to the backplane module drives the contactholder 162 from its closed position shown in FIG. 6 to its openedposition shown in FIG. 11, thereby opening the bypass circuits 152 a-152d. Later removal of the function module from the backplane moduleenables the spring assembly 174 to return the connector holder from itsopened position back to its closed position, thereby closing the bypasscircuits 152 a-152 d.

The backplane electrical connector 312 is located in a housing 314 ofthe function module 310. The function module housing has a flat bottomwall 316. The backplane electrical connector is aligned with an opening318 in the bottom wall that is sized to closely receive the housingcover 146 when plugging the backplane electrical connector into thefunction module electrical connecter. A lateral planar side wall 320 islocated along one side of the opening and extends upwardly towards thebackplane electrical connector. The side wall and the housing cover 146cooperate with one another in guiding relative movement of the functionmodule and maintaining alignment of the electrical connectors 114, 312when attaching or detaching the electrical connectors.

The function module 310 also includes conventional features that resistfurther movement of the backplane electrical connector 312 towards thefunction module electrical connector 114 after the connectors are fullyengaged with one another.

The function module bottom wall 316 includes a flat planar portion 322that is parallel with the top cover planar portion 144 when theelectrical connectors 114, 312 are being guided for attachment, areattached together, or are being detached from one another.

The actuators 182 are in the path of movement of the bottom wall portion322 when connecting the electrical connectors 114, 312. As theelectrical connector 312 first moves into the top cover receptacleportion 148, the bottom wall portion 322 engages and presses against thetop surfaces 184 of the actuators 182. Continued attachment movement ofthe function module 310 causes the bottom wall portion 322 to push theactuators into the housing and push the contact member 162 away from itsclosed position towards its opened position.

When the electrical connectors 114, 312 are fully engaged and connectedwith one another as shown in FIG. 11, the contact holder 162 has beenpushed by the function module 310 to the opened position as shown in thefigure. The bypass switch circuits 152 a-152 d are now open circuits andthe signal stream S extends through the function module 310 and not thebypass switch circuits.

Initial movement of the contact holder 162 away from its closed positiondoes not open the bypass switch circuits 152 a-152 d. Elasticdeformation of the spring arms maintains the contact noses 168 againstthe contact pads 156-158 during this initial movement. The contact nosesexhibit lost motion in the direction of contact holder movement duringthe initial movement of the contact holder from the closed positiontowards the opened position (other embodiments of the bypass switchassembly may include effectively no lost motion of the contact noseswith the contact member).

FIG. 6 illustrates the contact member 162 in its closed position butwith a spring arm 164 in its unstressed, relaxed shape. The lost motionof the contact noses 168 of the contact member is equal to the elasticdeformation of a contact nose from its unstressed position shown in FIG.6 to its actual shape with the contact nose pressed against a contactpad 156 or contact pad 158.

In the illustrated embodiment the electrical connectors 114, 312 makeelectrical connections with one another before the spring arm contactnoses 168 lose contact with the contact pads 156, 168. The functionmodule electrical connector mechanically engages the backplaneelectrical connector 314 along an initial mechanical engagement distance184 (see FIG. 11) before the electrical connectors 114, 314 electricallyconnect with one another. The function module electrical connector andthe backplane electrical connector continue being electrically connectedwith one another as the function module electrical connectormechanically engages the backplane electrical connector along asecondary mechanical engagement distance 186 until the electricalconnectors are fully mechanically engaged with one another.

The electrical connections between the function module electricalconnector 114 and the backplane electrical connector 312 of the functionmodule when attaching the function module to the function moduleelectrical connector are made during the lost motion phase of contactholder movement away from the closed position. The electrical connectionbetween the electrical connectors 114, 312 is made before the bypassswitch assembly 152 opens so as to assure no loss of signal continuitywhen attaching a function module.

When the function module 310 is removed from the backplane module 110,the compression springs 176 urge the contact holder 162 back to itsclosed position. The contact noses 168 re-engage the contact pads 156,158 before the contact holder reaches the closed position. The contactnoses exhibit the same lost motion in the direction of contact holdermovement during the final portion of movement of the contact holder fromthe opened position to the closed position. The electrical connectionbetween the backplane module and the function module is broken duringthe lost motion phase of the contact noses as the contact holder movesto the closed position for no loss of signal continuity when removing afunction module from the backplane module.

FIGS. 12-17 illustrate a second embodiment backplane module 110 a. Thebackplane module 110 a is similar to the backplane module 110 and soonly differences will be discussed. The same reference numbers used indescribing the first embodiment backplane module 110 will be used forcorresponding elements of the second embodiment backplane module 110 a.

In this embodiment the contact holder 162 of the bypass switch assembly150 pivots about a pivot axis rather than translating when movingbetween opened and closed positions. A side of the contact holder isattached to a shaft 186 integrally formed with the contact holder. Theshaft is rotatably mounted by snap or interference fits in spaced apartjournals 188. The shaft is coaxial with the pivot axis and extendstransverse to the DIN rail axis.

The shaft 186 permits the contact holder to pivot about the shaft axisand move from its closed position best seen in FIGS. 15 and 16 to itsopened position (shown in FIG. 20).

The bypass circuit 152 is closed when the contact holder 162 is in theclosed position. The bypass circuit is open when the contact holder isin the opened position.

The contact holder 162 has spaced-apart cross beams 189 a, 189 bparallel with the shaft 186. The cross beams are located on oppositesides of sets of contact pads 156, 158 located on the bottom surface 160of the printed circuit board 112. Each cross beam carries a pair ofspring contacts (164 a, 164 c) or spring contacts (164 b, 164 d). Eachspring contact has a pair of bent spring arms 166 that extend areside-by-side with one another and a contact nose 168 on each spring arm.The contact noses 168 of each spring arm makes contact with a respectivepair of contact pads 156, 158 to close the signal bypass circuit 152associated with the pair of contact pads.

The spring assembly 174 includes pairs of compression springs 176 thatapply torque to the contact holder 162 urging pivotal movement of thecontact holder 162 towards the closed position. The lower ends of thecompression springs are received in open-ended bores 178 defined by thehousing lower wall 128. The upper ends of the compression springssurround protuberances 180 extending downwardly from the contact holder.

The actuators 182 are located along a side of the contact member awayfrom the shaft and extend through the aligned through-openings in theprinted circuit board and the housing top wall. The openings are sizedto enable pivoting of the contact member without interference from theactuators rubbing on the sides of the openings.

FIGS. 12-17 illustrate the backplane module 110 a without a functionmodule attached to the function module electrical connector 114. Thecontact member 162 is in its closed position, the spring assembly 174pressing the contact noses of the spring contacts against the contactpads. One of the spring arms is drawn in FIG. 15 in its unstressed,relaxed state to show the amount of lost pivotal motion of the contactnoses (corresponding to the lost translation motion of the contact nosesof the first embodiment backplane module 110) when the contact memberpivots to or from the closed position.

FIGS. 18-20 illustrate the backplane module 110 a with the functionmodule 310 attached to the function module electrical connector 114. Thefunction module bottom wall portion 322 has engaged the actuators 182and caused the contact member 162 to pivot to the opened position. Thebypass circuit 152 is now open and the signal stream S extends throughthe function module electrical connector 114 and the backplaneelectrical connector 312.

When the function module 310 is removed from the function moduleelectrical connector 114, the springs 176 urge the contact member 162back to its closed position, closing the bypass circuit 152. The signalpath S extends through the bypass circuit and not through the functionmodule electrical connector.

The lost motion of the contact noses enables the same “make beforebreak” behavior of the electrical connectors 114, 312 and the bypasscircuits 152 as previously described for the first embodiment backplanemodule 110 when attaching or detaching the function module to thebackplane module 110 a.

The signal break in the signal stream S caused by removing a functionmodule from the network may differ in different network topologies.

For example, FIG. 27 illustrates a portion of an industrial controlnetwork 610 that includes a monolithic backplane 612. The backplane 612defines a portion of an Ethernet ring network topology that transmitsnetwork data along the backplane while providing network redundancy inthe event of a single signal break.

The backplane carries a head module 612 that communicates data betweenthe backplane and a PLC (not shown) and a number of function modules 614attached to function module electrical connectors (not shown) on thebackplane. The function modules write and/or read data to or from thering network. End modules 616, 618 close the ring topology at both endsof the backplane.

The backplane 612 and the end modules 616, 618 cooperatively define aring network signal path S consisting of a pair of rings R1 and R2 thatare each independently capable of transmitting data between the headmodule 612 and the function modules 614. The backplane 612 carries twosides of each of the rings R1 and R2 that are closed by the end modules.

If a single function module 614 is removed, the signal break caused bythe removal opens the rings R1 and R2 as shown in FIG. 28. An Ethernetswitch 620 in a function module adjacent to the signal break cantransfer data from one ring to the other ring to maintain signal pathcontinuity between the head module 612 and the attached functionmodules.

But should a pair of function modules 614 be removed from opposite sidesof an attached module 614 a as shown in FIG. 29, the signal path S isbroken on both sides of the attached function module 614 a. The functionmodule 614 a is stranded along the network and loses the ability tocommunicate with the head module 610 and the other function modules 614.

FIG. 21 schematically illustrates a printed circuit board 120 for abackplane module intended to form part of a modular backplane defining atwo-ring Ethernet network of the type shown in FIGS. 25-27. Thebackplane module includes a backplane switch assembly 150 identical tothe backplane switch assembly of the backplane module 110 or thebackplane module 110 a but intended to maintain signal continuity alongthe ring portions carried by the printed circuit board. To simplify thedrawing only the portions of the backplane switch assembly on theprinted circuit board 120 are shown in the figure.

The backplane module 110 b is similar to the backplane modules 110, 110a but is intended to define and form part of the two-ring Ethernetnetwork signal path S shown in FIGS. 25-27. The portions of the rings R1and R2 carried by the printed circuit board 112 are defined byconductive paths Sa, Sb, Sc, Sd that correspond to the four wires of aconventional four-wire Ethernet cable.

When a function module 310 is not attached to the function moduleelectrical connector 114, the backplane switch assembly 150 closes therings R1, R2 and maintains signal continuity across the break in bothrings caused by absence of the function module. When the function moduleis attached to the function module electrical connector the backplaneswitch assembly opens and the rings R1, R2 extend through the attachedfunction module.

Each electrical contact 164 described above have a pair of contact noses168 that make or break connections with a pair of contact terminals 156,158 on the printed circuit board. An alternative electrical contactconstruction is shown in FIG. 22. An electrical contact 164′, similar toan electrical contact 164, has one arm spring arm permanently attachedto the printed circuit board and the other spring arm being a free armwith a contact nose 168. The contact nose 168 makes or breaks contactwith a single contact terminal on the printed circuit board to close andopen the bypass switch circuit associated with the electrical contact.The contact nose 168 can also be designed with lost motion asillustrated in the figure.

An actuator 182 in possible embodiments is provided with multipleactuator members. FIG. 23 illustrates an electrical contact 164integrally attached to an actuator member 182′ that are formed from asingle stamping from a metal plate. Each electrical contact 164 of amulti-contact bypass switch assembly is in this embodiment integrallyattached to a respective actuator member 182′, the multiple actuatormembers forming the actuator. In the illustrated embodiment acompression spring 176′ (drawn in FIG. 23 with phantom lines insimplified form) surrounds the actuator member 182′ and is capturedbetween the top cover 144 and an enlarged upper end of the actuatormember. The spring urges the electrical contact towards its closedposition.

The function modules 310 are intended to pass the signal stream Sthrough the module. A “null module”, however, can also be attached toeither embodiment backplane module 110, 110 a, or 110 b. A null modulemechanically mates with the function module electrical connector 114 orthe housing receptacle 148 without forming electrical connections withthe function module electrical connector. The null module would notinclude structure that engages the actuators 182 and so attachment ofthe null module does not open the bypass circuit 152. A null module maybe used as a protective cover for the housing receptacle 148 or used forsome other purpose when the bypass circuit should remain closed.

Other embodiments of the bypass switch assembly may include more or lesspairs of contact pads depending on the conductive paths needed for thesignal type being carried by the backplane module, and the contact padarrangement may be different from those shown in the illustratedembodiments.

It is not necessary that the electrical contacts of a bypass switchassembly having two or more electrical contacts be identical with oneanother. If, for example, one of the electrical contacts transmits ahigh-frequency data signal, the one electrical contact may have featuresintended to minimize attenuation of the data signal transmitted throughthe contact, the other electrical contacts not including such features.

While this disclosure includes one or more illustrative embodiments of amechanical bypass switch assembly for carrying out the disclosed methoddescribed in detail, it is understood that the one or more embodimentsare each capable of modification and that the scope of this disclosureis not limited to the precise details set forth herein but include suchmodifications that would be obvious to a person of ordinary skill in therelevant art including (but not limited to) changes in materialselection, size, operating ranges (contact member travel, lost motion,and the like), environment of use, number and arrangement of contactpads, monolithic versus modular backplane construction, and the like, aswell as such changes and alterations for performing the disclosed methodthat fall within the purview of the following claims.

What is claimed as our invention is:
 1. A method for maintainingcontinuity of a network signal path extending along a backplane, thebackplane having a function module electrical connector attached to thebackplane being configured for selectively attaching or detaching afunction module to or from the backplane, the network signal pathextending through the function module electrical connector and throughthe function module when the function module is attached to the functionmodule electrical connector, the network signal path being open at thefunctional module electrical connector between first and second portionsof the network signal path of the backplane when the function module isnot attached to the backplane, the method comprising the steps of:providing a bypass signal circuit compatible with the network signalpath and being electrically connected in series with the first andsecond portions of the network signal path, the bypass signal circuitincluding a normally open circuit portion and an electrical contactmovable with respect to the bypass signal circuit; mechanically movingthe electrical contact being out of contact with the bypass signalcircuit into contact with the bypass signal circuit in response to thefunction module being detached from the function module electricalconnector and not in response to an electrical control signal, theelectrical contact when in contact with the bypass signal circuitclosing the bypass signal circuit and thereby enabling the bypass signalcircuit to close the network signal path between the first and secondportions of the network signal path; and mechanically moving theelectrical contact being in contact with the bypass signal circuit outof contact with the bypass signal circuit in response to the functionmodule being attached to the function module electrical connector andnot in response to an electrical control signal, the bypass signalcircuit being open when the electrical contact is out of contact withthe bypass signal circuit whereby the first and second portions of thenetwork signal path are electrically connected by the network signalpath extending through the function module electrical connector and thefunctional module and not by the bypass signal circuit.
 2. The method ofclaim 1 wherein the step of mechanically moving the electrical contactout of contact with the bypass signal circuit comprises transmitting aforce from the function module to the electrical contact.
 3. The methodof claim 2 wherein the step of transmitting a force from the functionmodule to the electrical contact comprises the function module engagingand displacing an actuator connected to the electrical contact forconjoint movement with the electrical contact.
 4. The method of claim 1wherein the step of mechanically moving the electrical contact out ofinto contact with the bypass signal circuit comprises relieving a forcebeing transmitted from the function module to the electrical contact. 5.The method of claim 4 wherein the step of relieving a force beingtransmitted from the function module to the electrical contact comprisesmoving the function module out of contact with an actuator connected tothe electrical contact for conjoint movement with the electricalcontact.
 6. The method of claim 1 comprising the step of transmitting aforce from the function module to the electrical contact maintaining cthe electrical contact out of contact with the bypass signal circuitwhile the function module is attached to the function module electricalconnector.
 7. The method of claim 6 wherein the step of transmitting aforce from the function module to the electrical contact comprisesmaintaining the function module against an actuator rigidly connected tothe electrical contact.
 8. The method of claim 1 comprising the step ofrelieving a force being transmitted from the function module to theelectrical contact when detaching the function module from the functionmodule electrical connector whereby the electrical contact moves intocontact with the bypass signal circuit.
 9. The method of claim 8 whereinthe step of relieving a force being transmitted from the function moduleto the electrical contact comprises moving the function module out ofcontact with an actuator connected to the electrical contact forconjoint movement with the electrical contact.
 10. The method of claim 1comprising the step of continuously applying a force to the electricalcontact urging the electrical contact into contact with the bypasssignal circuit.
 11. The method of claim 10 wherein the force applied tothe electrical contact urging the electrical contact into contact withthe bypass signal circuit is generated by a spring.
 12. The method ofclaim 1 wherein the network signal path comprises multiple conductivepaths and the bypass signal circuit comprises multiple conductive paths,each respective conductive path of the network signal path beingelectrically connected with a respective conductive path of the bypasssignal circuit when the bypass signal circuit is connecting the firstand second network signal path portions.
 13. The method of claim 12wherein the multiple conductive paths of the network signal path and themultiple conductive paths of the bypass signal circuit each comprisefour signal paths corresponding to the four wires of a 4-wire Ethernetcable.
 14. The method of claim 1 wherein the network signal path alongthe backplane comprises multiple conductive paths, and the electricalcontact comprises multiple electrical contact members, each respectiveconductive path of the network signal path being electrically connectedwith a respective contact member of the electrical contact when thebypass signal circuit is connecting the first and second network signalpath portions.
 15. The method of claim 1 wherein the backplane comprisesa plurality of backplane modules, the function module electricalconnector being attached to one of the plurality of backplane modules.16. The method of claim 1 wherein the network signal path along thebackplane is a portion of a ring network.
 17. The method of claim 1wherein the network signal path along the backplane is a portion of alinear network.
 18. The method of claim 1 wherein detaching the functionmodule from the function module electrical connector breaks anelectrical connection between the function module and the functionmodule electrical connector, and the electrical contact moves intocontact with the bypass signal circuit in response to detaching thefunction module from the function module electrical connector before thebreaking of the electrical connection.
 19. The method of claim 1 whereinattaching the function module to the function module electricalconnector makes an electrical connection between the function module andthe function module electrical connector, and the electrical contactmoves out of contact with the bypass signal circuit in response toattaching the function module to the function module electricalconnector after the making of the electrical connection.
 20. The methodof claim 1 wherein the electrical contact includes a contact nose, andthe step of mechanically moving the electrical contact into contact withthe bypass signal circuit comprises lost motion of the contact nosebeing engaged against the bypass signal circuit while moving theelectrical contact into contact with the bypass signal circuit, and thestep of mechanically moving the electrical contact out of contact withthe bypass signal circuit comprises lost motion of the electricalcontact being engaged against the bypass signal circuit while moving theelectrical contact out of contact with the bypass signal circuit.